Brewed up a batch of pale ale a few weeks ago. Hit all my numbers going in. Mash temp - 154, volume was right on, OG was 1.062.

Just a s predicted by Beer Smith.

Made a big 1056 starter, split between 2 fermenters. It kicked off quickly.

Only issue was fermenter temperature - had a hard time keeping it below 72, and I know it was in the mid 70's for a bit.

Checked gravity last week at 1.021 . . . a bit higher than I was expecting and let it go another week.

Transferred to secondaries this weekend for dry hopping - no change in gravity.

I've pulled a bit out, dry hopped and carbonated in a 2 liter bottle. It tasted good, no bad flavors, just a little watery mouth feel and low gravity.

I'm wondering if I should just continue with the dry hopping and bottle, treating it as a session beer, or mix up a little light DME and add to see about jump starting the yeast again and lower the gravity.

Did the 154 mash temperature bring out too many un-fermentables or did the warm fermenter stall the process?

The warmer temperatures would probably accelerate the fermentation process, not kill it. Most pale ale yeasts are comfy in the 70s. Not super high 70s, but room temp should be fine.

At this point you should not do anything to the beer IMO. Your beer clocks in at 5.5% ABV, hardly a session beer. That's not a super high FG. It's a few points high but really not too bad. Perhaps work harder on keeping a cooler fermentation temp, but this time I'd leave the beer as is.